macro_rules! assert_ansi_string {
($string:expr, $hspace:expr, $vspace:expr, $overflow:expr, []) => { ... };
($string:expr, $hspace:expr, $vspace:expr, $overflow:expr, [$($segment:tt),*]) => { ... };
(@verify_segment $seg:expr, { $($field:ident => $value:tt),* }) => { ... };
(@check_field $seg:expr, len, $expected:expr) => { ... };
(@check_field $seg:expr, txt, $expected:literal) => { ... };
(@check_field $seg:expr, rst, $expected:expr) => { ... };
}